The present invention relates to image stabilization in medical imaging. An imaging position is stabilized with respect to a region of interest as images are acquired over time.
In medical diagnostic ultrasound imaging, a transducer is positioned adjacent to a patient. The sonographer attempts to maintain the transducer in a given position relative to a region of interest within the patient. Temporal variations in the transducer position due to movements by the sonographer, movements by the patient, breathing motion, heart motion or other sources of motion cause the transducer to move relative to the patient. The scan plane is typically fixed at least in the elevation dimension with respect to the transducer. The undesired or unintended motion results in scanning different tissue within the patient.
Images may be stabilized within the scan plane. Motion between subsequent images in a sequence of images is tracked. The acquired image data is then adjusted or shifted along the azimuth or range dimensions so that a region of interest is maintained at the same location on the display. Other processes, such as contrast agent quantification, use motion tracking to reduce motion artifacts. Previously acquired data is processed or shifted as a function of the motion to reduce the artifacts. However, some motion artifacts may remain despite shifts in data. The shifted data may not optimally represent the region of interest. To provide the maximum versatility, a large amount of unused image information is acquired and stored for allowing shifts. Acquiring lots of ultrasound information may reduce frame rates.
Motion tracking is also used in three-dimensional and extended field of view imaging. A plurality of two-dimensional scans are performed in different positions within a same plane for extended field of view imaging. The motion between the various acquired images is determined for assembling the images together in an extended field of view. Similarly for three-dimensional imaging, a plurality of two-dimensional images are acquired for a plurality of scan planes within a three-dimensional volume. Motion tracking is performed using ultrasound data, motion sensors on the transducer or other techniques for determining the relative positions of the scan planes. An image representing three-dimensional space is then rendered from the acquired sets of ultrasound data. However, multiple images or sets of data are acquired to form the extended field of view or three-dimensional representation.
Another motion adaptive process is disclosed in U.S. Pat. No. 5,873,830. An amount of motion between different images is detected. Where motion is not detected or minimal, the beamformer is configured to increase spatial resolution, such as by increasing line density or the number of transmit beams. Where motion is detected, the frame rate is increased by decreasing the line density or number of beams. However, changing density or number of beams as a function of detected motion may still result in desired tissue fading in or fading out of the image scan plane due to the motion.